High-Order Sliding Mode Control for the Test Mass stabilization of the LISA MIssion: preliminary results

The main objective of this paper is the design of a controller for the test mass release of the Laser Interferometer Space Antenna (LISA) mission. Since the test masses are used as sensors in the science phase for environmental measurements, the control system can be able to robustly deal with large initial deviations of the release mechanism. Moreover, the control system should be able to maintain and stabilize the test masses with a precision. For this reason, two Sliding Mode Control (SMC) are included in this study. A second-order SMC is mainly proposed for this critical phase, which is able to handle uncertainties and noise introduced by the sensors system. This controller is compared with a first-order SMC, which was used in LISA Pathfinder mission, in terms of accuracy and stead-state error. A nonlinear orbital simulator is considered in the simulations, with limitations both of the actuation system (with saturation and delay) and of the update frequencies. Model uncertainties, different initial conditions and external disturbances are also included in the performed simulations.